So I completed the app and it worked exactly how it is supposed to. I decided to play around to see if there were any parts I could change using knowledge I already knew, and that is when I ran into this weird problem.

struct Activity: Codable, Identifiable, Equatable {
    var id = UUID()
    let title: String
    let description: String
    var completedCount = 0

    static func ==(lhs: Activity, rhs: Activity) -> Bool {
        lhs.id == rhs.id
    }
}

The method that updates the count for each activity:

    func increment(activity: Activity) {
        var copy = activity
        copy.completedCount += 1
        if let index = activities.firstIndex(where: { $0 == activity }) {
            print("Index found at ", index)
            activities[index] = copy
        }
    }

See after adding my own method to check for equality it stopped working! when I increment the counter UI doesn't change, no matter how many times I increment it. But when I relaunch the app I see it has incremented by 1.

Does anybody have any idea what is going on? Because if I remove the static equality method it works again.

Hi, The thing is that out of the box the == operation checks every property you have for equality (ie. id, title, description, ect...), when you override the function it no longer does that it only checks the ones you specify (ie. id, in this case) with the lhs.id == rhs.id, so when you change the Activity’s count the change is not published because it only checks the id, now the change still happens so when you restart the app you see the change, so one way of fixing this is adding " && lhs.completedCount == rhs.completedCount" to the == function.

static func ==(lhs: Activity, rhs: Activity) -> Bool {
        lhs.id == rhs.id && lhs.completedCount == rhs.completedCount
    }

Thanks but I'm a little confused. I thought the Equatable conformance was just to to find the location of the item we want to edit in the array? so this line finds the item:

if let index = activities.firstIndex(where: { $0 == activity }) { ... } 

and this line changes the array which is marked with @Published which should trigger the UI to update.

activities[index] = copy

Behind the scenes the activitties array is using the == to check for changes, you could also add a new UUID to the copy when you update the completedCount and it will update the view.

func increment(activity: Activity) {
        var copy = activity
        copy.completedCount += 1
        copy.id = UUID()
        if let index = activities.firstIndex(where: { $0 == activity }) {
            print("Index found at ", index)
            activities[index] = copy
        }
    }

Thank you both, that makes sense and I understand it now 👍